Question

If, $S\left(g\right)+e^{-}\to S^{-}\left(g\right),\Delta H=-207.6kJ$

$S\left(g\right)+2e^{-}\to S^{2-}\left(g\right),\Delta H=+335.2kJ$

The enthalpy for the reaction $S^{-}\left(g\right)+e^{-}\to S^{2-}\left(g\right)$ is:

• A. +127.6 kJ
• B. -127.6 kJ
• C. +542.8 kJ
• D. -641.8 kJ

Answer 1

The correct option is C +542.8 kJ

Given that,

$S\left(g\right)+e^{-}\to S^{-}\left(g\right);\Delta H=-207.6kJ$
$S\left(g\right)+2e^{-}\to S^{2-}\left(g\right);\Delta H=335.2kJ$
Now,
(i) $S^{-}\left(g\right)\to S\left(g\right)+e^{-};\Delta H=207.6kJ$
(ii) $S\left(g\right)+2e^{-}\to S^{2-}\left(g\right);\Delta H=335.2kJ$
Adding (i) and (ii), we get
$S^{-}\left(g\right)+e^{-}\to S^{2-}\left(g\right);\Delta H=207.6+335.2$ $=542.8$ kJ